The present disclosure relates to semiconductor-on-insulator (SOI) structures, and more particularly to a radiation hardened SOI structure and a method of fabricating the same.
Semiconductor-on-insulator (SOI) structures offer inherent improved radiation hardness over their bulk semiconductor counterparts. Despite the improved radiation hardness, SOI structures when used in a harsh total dose environment are still prone to radiation-induced failure due to charge build-up in the buried insulator layer. The charge build-up leads to degradation of device characteristics due to significant threshold voltage shift, increased leakage current and poor sub-threshold characteristics.
The prior art suggests implantation of acceptor-type dopants such as, for example, boron to mitigate the threshold voltage shift. Nevertheless, this prior art approach is not acceptable for thin-body silicon channel devices such as extremely thin semiconductor-on-insulator (ETSOI) and FinFET devices. Additionally, the prior art approach mentioned above does not provide full immunity for long-term use in harsh environments.
In order to further improve the radiation hardness of SOI structures, there have been proposed approaches to implant the buried insulator layer with ions such as nitrogen, aluminum, boron, arsenic, silicon and germanium. Nonetheless, implanting the buried insulator layer of the SOI structure will however complicate the device fabrication process, while the use of such schemes may wind up to be impractical for thin-body SOI structures. This will require implanting the buried insulator layer through the top semiconductor active layer, thereby generating substantial crystal defects within the top semiconductor active layer and damaging the interface between the buried insulator layer and the top semiconductor active layer. High temperature anneal steps are subsequently required to remove the crystalline damage due to implantation. Although high-temperature annealing will improve the crystalline quality of the top semiconductor active layer and its interface with the buried insulator layer, it may not fully recover the crystalline quality of the top semiconductor active layer thus degrade the transport properties in the top semiconductor active layer. Moreover, the requirements for using high dose can lead to amorphization of the top semiconductor active layer in thin-body SOI structures. Implanting the buried insulating layer through the top semiconductor active layer will additionally limit the choice of ions to those which are either inert in the semiconductor material of the top semiconductor active layer or dopant atoms in the top semiconductor active layer.
In view of the above, additional improvements in radiation hardness are desirable for long term usage of SOI structures in harsh environments such as, for example, outer space, nuclear reactors and particle accelerators. Additionally, improved radiation hardness is growing increasingly used as semiconductor processing becomes more radiative. For example, processing techniques such as reactive ion etching and plasma etching may introduce radiation damage into a semiconductor structure.